The hot water extraction process for recovering bitumen from oil sand has been extensively described in the prior art. In general this process, as embodied in applicant's plant, involves:
Mixing the oil sand with hot water and a small amount of caustic in a rotating horizontal drum (called the "tumbler"). The tumbler has a slight downward tilt so that the mixture moves longitudinally therethrough over a retention period of about 3 minutes. Rotation of the tumbler causes cascading of the mixture, with the result that air bubbles are entrained in the slurry. In the course of this mixing step, bitumen is heated, separated from the sand grains and dispersed into the water phase in the form of small flecks. Some of these flecks become aerated by contacting and coating air bubbles;
The slurry exiting the tumbler is diluted with additional hot water;
The diluted slurry is temporarily retained in a vessel referred to as a primary separation vessel ("PSV"). This vessel is open-topped and has a cylindrical upper end and a conical lower end. The slurry is retained in the vessel for about 45 minutes under generally quiescent conditions. In the course of this step, some of the bitumen that has been sufficiently aerated rises and forms froth which overflows the lip of the vessel and is collected in a launder and is recovered. This aerated froth is referred to as "primary froth". Sand in the slurry settles and is removed through a bottom outlet of the PSV as a tailings stream. A watery "middlings" stream containing some fine solids and bitumen is removed from the PSV mid-section;
The middlings and tailings are combined and subjected to aeration and flotation in a tailings oil recovery vessel ("TORV") in accordance with U.S. Pat. No. 4,545,892. The TORV recovers additional bitumen or oil in the form of what is referred to as post-primary froth; and
Middlings from the TORV may be subjected to intensive aeration, impeller mixing and flotation in a series of flotation cells to recover residual bitumen in the form of a "secondary" post-primary froth.
The primary, TORV and secondary post-primary froth streams each contain bitumen (or oil), water, solids and air. The contamination with water and solids increases through the sequence of primary, TORV and secondary froths.
To closely control and fine tune the extraction process, it is highly desirable to be able to determine the relative amounts of oil, water and solids in the streams of aerated froth, on a virtually instantaneous basis which lends itself to automatic on-stream implementation.
In the past, the system used has involved taking froth grab samples and analyzing them by soxhlet extraction for oil, water and solids contents. The problem with this system is that the results of the analysis are not obtained until many hours after taking the sample. Since the nature of the oil sand feed and the composition of the produced froth streams vary constantly, the analyzed composition data are little help in controlling the variables involved with the process (such as caustic additions), to fine tune it to the current throughput. As a result, variable control has been an art that greatly depended on the skill and experience of the operators, who primarily have depended on visual assessment of the process.
There has therefore long existed a need for a method for quickly and continuously establishing the composition or quality of the aerated bitumen froth. It is the object of this invention to provide such a method.